Worm generating hob



o. G; slMMQNs 1,765,853

June 24, '1930.

' woRM GENERA'TING HOB Filed Aug, 27, 1927 5 Sheets-Sheet 2 Hun llllll June 24, 1930. o@ G. SIMMONS `1,765,853

WQRM GENERATING HOB Fiied Aug. 2'?, .1927 5 sheets-sheet 3 ELLE stares rarer-ar o @LIVER SIMMNS, F LMLWOD, R10, ASSIGNOR TQ THE NTNAL TOQL COM- FANY, F CLEVELNJD, 9R10, A CORPORTGN 0F OHIO WORM GENERATNG HOB .application led August 27, i927, Serial No. 215,970.

g provide a hob in which successive teeth cut to increasing depth and Width into a vv'orm blank and in which the final or finishing tooth is formed to accurately generate the opposite 'faces of adjacent Worm teeth and further to provide a hob in which the teeth make suhstantially parallel cuts in the blank, each slightly deeper and Wider than that of the preceding tooth, so that the groove or grooves in the olanlr are gradually and uniformly enlarged to the correct vvidth, depth and contour.

A -further object oit the invention is to )provide a hoh having its teeth arranged in a helicoidal spiral curve and in which the opposite side faces of the teeth lie in surfaces of revolution which may he generated by means oi' a cutting element, which during the cutting operation has relative angular and translative movements with respect to the hlanlr, the relative angular and translative movements being such as may he readily produced hy mechanisms such as are Well known to those skilled in the art for imparting suitably correlated rotary and linear movements.

A further object or the invention is to provide a hoh in which the teeth are all of suhlstantially the same size and shape and so 'formed as to have ample strength to withstand the stressesto which they are subjected in use. u

vl'n order to provide proper rolling contact between Worm teeth and worm gear teeth` throughout the Width of the Worm gear, it is essential that each tooth tace of the worm conform to a surface of revolution which., within the confines of the tooth surfaces, intersects cylindrical surfaces coaxial with the worm along helices having the same longitudinal lead. lf this condition he fulfilled,

` the contours of the Worm teeth are uniform intersection of a tooth face with planes parallel vvith the axis, all advance in said planes at the same rate so that the worm teeth may coact with teeth of a properly generated Worm gear in the manner of a rack with a gear.

l The present invention has for an important object to provide a generated hoh in Which the generating cutting edges are so disposed that they will produce truly helical Worm teeth of the desired uniform contour in axialy planes and in which the generating cutting edges simultaneously cut opposed tooth faces to accurately conform to helical surfaces ci revolution.

il. further object is to provide a Worm generating hoh which can he sharpened hy grinding away the iront laces of the teeth without aiectng the 'form or" kWorin teeth generated Toy the holo. i

llith the alcove and other ohjects in vievv,

the invention mayhe said to comprise the hoh as illustrated in the accompanying drawings hereinafter described and particularly set 'forth in the appended claims together with such variations and modifications thereof as will he apparent to one skilled in the art to which the invention appertains.

Reference should he had to the accompanying drawings forming a part of this speciication in which Fig. l is a perspective view showing the hob operating upon a Worm blank.

Fig. 2 is a top plan view of the holo and Worm blank.

Fig. 3 is an end elevation of the hoh.

lllig. d is a plan view of the holo.

Referring to the accompanying drawings, the hob is formed upon the huh i, which is provided with an axial hore 2 having a he Way 3, formed therein so that the hoh may e iixed to the holo spindle oi a suitable hohhing machine. ln cutting the holo teeth, the end 4 of the huh is reduced to tapered form as clearly shown in Fig. l of the drawing. `The cutting teeth of the hob which are numbered from 5 to 20 in 'the drawing extend around the axis of the hob in a helicoidal spiral curve which has a uniform lead longitudinally of the axis and'also a uniform rate of advance fn n or lead laterally of said axis. A cutting tooth 5 is located at the forward end of the helicoidal spiral row of teeth and from the tooth 5 to the tooth 20, the distance of the teeth from the axis of the hob graduallyv increases due to the lateral lead of the helicoidal spiral curve followed by the teeth. For instance, the root or base lines of the hob teeth which are indicated at 2l and 22 in Fig. 4 of the drawing, lie on the surfaceof a cone and are helicoidal spiral curves such as would be generated on the conical surface if the cone were revolved about its axis at a uniform angular speed and a point on its surface were moved in a radial plane along the cone surface at a uniform rate, the taper of the cone giving the point a uniform rate ofy advance or lead laterally of the axis, as it is moved longitudinally thereof.

The teeth of the hob are in the form of segments of a` helicoidal spiral worm tooth, the

cross-sectional contour of which is uniform` in radial planes, each face of the worm tooth coinciding with surfaces of revolution formed by a linear generatrix lying in an axial plane and moving about said axis Without movement other` than that of translation with re- `it is desired to generate with the hob. As

shown in Figs. 2 and 4, the oppositeA faces of the hob teeth conform to a surface of revelution in whichthe helicoidal spiral root curves 2l and 22 lie, the opposite faces 23 and 24 of the teeth being generated outwardly of the root lines by a generatrix passing through the axis and/root curve. The outer edges 25 of the teeth are relieved to provide proper cutting clearance and the teeth are separated by radial gashes 26 providing cutting edges 27 and 28 at the opposite edges of the front faces of the teeth which lie in axial planes, and in the generated surfaces of revolution of theopposite side faces of the teeth. As shown herein, the surfaces of revolution in which the opposite side faces 'of the hob teeth lie have a straight line generatrix vand the cutting edges are therefore straight. The -side faces of such a hob may be generated by a cutting tool having a straight cutting edge disposed in an axial plane and having `uniform linear movement laterally of the axis of a uniformly.. rotating hob blank as well as uniform linear movement longitudinallythereof during the cutting operatlon.

The eneratrices of the opposite side faces of the ob teeth are disposed at equal and opposite inclinations with respect to thel hob axis so that'the cutting edges of the teeth until it is which lie in axial planes have equal and opposite inclinations with respect t0 the axis, the cutting edges of each tooth being symmetrically disposed with respect to the planes perpendicular to the hob axis. The rates of linear movements of the generatrices of'opposite faces of the hob`teeth are at such ratios to the angular movements thereof in generating the curves of the opposite sides of the teeth, that the helicoidal spiral curves traced by the generatrices on a given base cone are parallel so thatoutwardly of this base cone, the hob teeth will be of uniform size and shape in radial cross section. The helicoidal spiral curveson the base cone forming the root lines of the teeth have uniform leads longitudinally of the axis' of the hob and laterally thereof. If the helicoidal spiral curves ofthe side faces of the teeth were continued outwardly to the line of intersection, the line of intersection would also be a helicoidal spiral curve having uniform lead longitudinally of the axis and laterally thereof, the projections of all of the above mentioned helicoidal spiral curves ina plane perpendicular to the axis being Archimedean s lrals.

In operation, the s ort tooth 5 of the hob first engages the forward end of the worm blank and the hob is rotated in thedirection to gradually bring the teeth of greater cutting radius into engagement with the blank. The rotation of the blank is in the same direction as that of the hob and the hob is given a feed movement longitudinally of the blank proportional to the rate of angular movement of the blank and corresponding to the lead of the helical curve of the teeth to be generated on the blank. As the successive teeth engage in the groove on the blank, the groove is Gradually deepened and widened Ibrought to its final form by the finishing tooth 20.

In generating a worm with the hob, the hob spindle is preferably at an angle ,to the axis of the blank such that the portions of its thread adjacent the blank extend substantiallyin the direction of the threads to be cut and at the distance from the lblank axis necessary to obtain the desired depth of cut, and with the finishing tooth 20 substantially centered with respect to the blank. The hob is first positioned with the small tooth 5 at the forward end of the blank and with the larger teeth beyond the end of the blank. The hob is then rotated rapidly. and the blank turned slowly and advanced with respect to the hob at a rate proportional to its turning movement. Successive teeth of the hob arethus brought into engagement with the blank cutting a groove which is graduallywidened and dee ned by each successive tooth until the finishing tooth 2O has passed through the groove., As the worm is slowly turned and the hob lslowly advanced along the blank in the direction of its axis,

each tooth engages successive portions of the blank until the helical teeth extend the desired length along the blank. i i A What I claim is:

1. A worm generating hob having circumferentially spaced cutting teeth of substantially uniform size and shape in axial cross sectoin and extending around the hob axis inl a helicoidal lspiral curve, each tooth having ferentially spaced cutt1n .its cutting edges lying in an axial plane and at opposite and substantially equal'inclinations with respect to a plane perpendicular to the axis of the hob.

2. A worm generating hob having circum- '1'5' ferentially spaced cutting teeth formed by 'transverse gashes in a helicoidal spiral worm thread, each face of which has a contour corresponding to a surface of revolution gene- .rated by a straight line generatrix disposed at a fixed angle to an axls of revolution and moving about said axis along a helicoidal spiral path having auniform lead longitu-' dmally and also laterally with respect to said axis, intersecting generatri'ces' ofy opposite. side faces of the teethy being symmetrically disposed with respect toa plane perpendicular to said axis. I a

3., A worm generating hob having circumteeth formed by transverse gashes in ahehcoidal spiral worm thread, the faces of which have contours corresponding to surfaces of revolution genef rated by straight line generatrices intersect# ving an 'axis of revolution at substantially equual and opposite angles' and moving .about said axis at xed angles'thereto along helicoidal spiral paths having uniform leads longitudlnally and also laterally with respect to said axis.

'4. A worm generating hob having circumferentially spaced cutting teeth extending aroundthe' axis of the-hob in a helicoidal ferentially spaced cuttin teeth of substantially uniform size and s ape in laxial cross section extending around the axis of the hob in a helicoidal spiral curve, the outermost toothhaving stralght outwardly converging cutting edges on opposite sides thereof, the other teeth of the hob having converging cuttin edges which travel in paths parallel wit the first mentioned tooth at gradually decreasing distances from the axis of rotation, said teeth having relieved peripheral faces which intersect axial planes in lines parallel with the axis of revolution.

-In testimony whereof I aix my signature.

' OLIVER G. SIMMONS.

spiral curve', each tooth of the hob having posite sides thereo dis osed at substantial equal and 'opposite ang es with respect to the hob axis, the other teeth of the hob having converging cuttin edges which travel in paths parallelwit `the paths of the cutting edges of the first mentioned tooth at gradually decreasing distances from the axis of rotation.

6. Aworm generating hob having circumpaths of the cutting edges of the 

